How does foam aluminum unlock automotive aluminum?

[china aluminum industry network] this year, one said that car black technology can not talk about lightweighting. When we talk about lightweight, we must say aluminum alloy. When it comes to aluminum alloys, even its way comes with the same door-to-door squeezing as the neighbor Li Xiaozi: Isn't it the use of stamping technology to make aluminum alloy sheets and use casting technology to make cast aluminum parts?

Too young. There are many ways to unlock aluminum alloys, such as aluminum foam.

Foam aluminum history

In the car circle, there is such a material. Like a foam, it has a large porosity, a high specific surface area, and a strong damping and damping. Like a metal, it has a higher specific strength, a higher specific rigidity, a higher temperature resistance, and a lighter quality. It is a real dreamer for a carmaker.

But you are not dreaming. As early as the late 1940s, the United States took the lead in studying this material, and in 1951 scientists Elliot pioneered the successful production of aluminum foam.

Aluminum foam is a kind of lightweight porous metal material containing numerous air bubbles in aluminum matrix. It also has the characteristics of metal phase bubbles. It is a kind of physical functional material with broad application prospects.

The main structural features

(1) The pore structure is adjustable. Can be divided into two kinds of situations: one is with independent hole structure, scattered bubbles or hollow particles are distributed in the metal matrix (some people call it sponge aluminum); the other is a hole structure with a through hole (some call it Honeycomb aluminum).

(2) Larger aperture. The range of change is 0.1 - 10.0 mm (in general powder metallurgy porous metal pore diameter not more than 0.3mm).

(3) The void rate is high. The range of variation is 40% to 90% (general void ratio of powder metallurgy porous metal is no more than 30%).

(4) Small density. The change range is 0.2-0.9/cm3 (only 1/10-1/3 of the same volume of aluminum).

However, this material is difficult to control in the foaming process, foam size and uniformity, production is very difficult, and was not widely used at that time, and in the following 40 years, the manufacture and application of foam aluminum has been in a state of stagnation. . Until the end of the 1980s, the Kyushu Institute of Industrial Technology in Japan improved the production technology of foamed aluminum, and the boom in the development of foamed aluminum materials was once again on the international stage.

The previous world foam metallurgy conference held in Bremen, Germany in 1999 was a landmark event for aluminum foam. Since then, aluminum foam has moved from behind the scenes to the stage in the true sense of the word, and the level of industrialization is also getting higher and higher. It is no longer the scientific research material that nobody in the laboratory cares about.

Main performance characteristics

High damping performance and impact energy absorption rate: The damping performance is 5-10 times that of metallic aluminum. When foamed aluminum with a porosity of 84% undergoes 50% modification, it absorbs energy of 2.5 MJ/M3C or more.

Good acoustical function: 1. Sound insulation performance (closed-cell): When sound wave frequency is between 800-4000HZ, the sound insulation coefficient of closed-cell aluminum foam is more than 0.9. 2. Sound absorption performance (micro-vias and through-holes): When the sound wave frequency is between 125 and 4000 Hz, the sound absorption coefficient of the through-hole aluminum foam can reach 0.8, and the average absorption coefficient of the octave exceeds 0.4.

Excellent electromagnetic shielding performance: When the electromagnetic wave frequency is between 2.6-18 GHZ, the electromagnetic shielding of aluminum foam can reach 60-90dB.

Good thermal performance: Through-hole aluminum foam has good heat dissipation under forced convection conditions because its pores communicate with each other. Does not burn and has better heat resistance. Corrosion resistance, good weather resistance, low moisture absorption, no aging, no toxicity.

Easy to process: easy to cut, drill, cement; can be bent into the desired shape after molding; can be surface treatment with organic or inorganic paint; can be two sides of the skin, constitute a large size of light, high stiffness plate.

Easy to install: Foam aluminum material can be installed at a height without mechanical lifting equipment, such as ceilings, walls, roofs, etc., can be mechanically connected or fixed directly with screws, or glued to the wall with adhesives. Or on the ceiling.

Metal sheet - foamed aluminum - "sandwich" structure formed of metal sheet inherits the excellent performance of foamed aluminum, and has a high bending strength, can be used as a new type of building materials, high stiffness structural parts of locomotives and vehicles.

Foam aluminum preparation method

There are more than 20 kinds of aluminum foam preparation processes, and the fields involved are very wide. However, for the automotive industry, aluminum foam prices are not cheap, the processing technology is also more complicated, and the stability and reproducibility of various preparation processes are not very high. The problem of non-uniform pore structure has not yet been completely solved.

Foamed aluminum is mainly prepared by solidification method, sintering method, deposition method, etc. Among them, the solution foaming method is relatively simple, the pores are controllable, and the cost is low, which is more suitable for the large-scale production of foam aluminum materials with large specifications.

Aluminum foam in the automotive industry

Due to its characteristics of light weight, high specific strength, high specific stiffness, damping, shock absorption, heat insulation, and battery shielding, foam aluminum is used in aerospace, high-speed chips, and building materials. In recent years, this material has been used. It gradually entered the automotive sector.

One of the classic applications for foamed aluminum is the foamed aluminum sandwich structure. Due to the combination of foamed aluminum and sheet metal properties, this structure has better strength, stiffness is more than doubled, damping and anti-collision ability is improved by more than 3 times, and the same quality. Greatly reduced.

OME company once designed a car with a foamed aluminum sandwich panel structure. After using this material, it can reduce the weight by 25% under the same structure.

According to reports, if aluminum foam parts replace conventional automotive castings, the mass can be reduced by more than 50% without changing the strength of the parts.

Prior to this, BMW had teamed up with the Australian Light Metal Performance Research Center (LKR) to develop a foam aluminum structure engine mount that can increase chassis stiffness and improve frame stability while also dissipating mechanical oscillations and thermal energy.

The German Kaman Automobile Company uses sandwich foam aluminum to manufacture the top cover of the Ghiaroadster. While the quality is reduced by 25%, the rigidity is about 7 times larger than the original steel structure. This is really one stone and two birds.

When aluminum foam is used as an energy-absorbing buffer structure, it is mostly used in energy-absorbing boxes, door beam structures, and bumpers, and can achieve the purpose of buffering and absorbing energy. For example, using foamed aluminum as a sandwich core to produce a bumper for cars has the function of absorbing impact kinetic energy. Since the rebound rate is very small (less than 3%), secondary collision damage can be effectively avoided.

Let's talk in more detail about the more unfamiliar items:

Energy absorber box

The energy absorbing capacity of the filling structure is greater than the sum of energy absorbed by the energy absorption box and the foam aluminum alone, and due to the isotropic nature of the foamed aluminum, good energy absorption can also be obtained in the offset collision.

With the improvement of people’s safety awareness, the concept of pedestrian safety has gradually taken shape. This kind of structure can completely absorb all the energy that the vehicle hits at a speed of 15Km/h, and it can protect the safety of pedestrians.

NVH

On the heat-absorbing sound insulation, foamed aluminum can also have an immediate effect. For example, it was used in a passenger car silencer.

Passenger car foam muffler, foam aluminum sound-absorbing board after fire treatment, can be applied in the exhaust temperature of nearly 600 °C. The noise reduction effect is 2-3 times that of the impedance-type noise elimination core and the parallel resonance-type noise reduction inner core muffler, and the weight is reduced by about 1/3.

In addition, the use of foamed aluminum materials for the production of car floors, partitions, door sandwich panels, etc. can also achieve the effect of sound insulation, vibration isolation.

Top cover

The top cover of a car is used as a cover for a large area of ​​a car. How to integrate the weight and strength requirements has always caused headaches for manufacturers. The use of foam aluminum sandwich panels, the thickness of only about 2mm, rigidity 7 times the steel plate roof, the weight can also reduce more than 50%.

Expectations for the future

Of course, things that look perfect do have the disadvantages that make people feel helpless. At this stage, the advantages of aluminum foam are not superior to high costs.

In the future, the use of a separate aluminum foam structure in automobiles may encounter bottlenecks, but it may be instructive to combine this material with other materials such as metals and polymers.

For example, the combination of foamed aluminum and aluminum alloy or carbon fiber composite materials can relieve the disadvantages of high cost, brittleness, and breakage of carbon fiber materials to a certain extent, and at the same time, they can obtain good thermal insulation and high temperature resistance.

The reverse is also the same, the use of carbon fiber as a supplementary material in foam aluminum, to improve the performance of aluminum foam itself is also very promising. Now that there have been some studies on carbon fiber-reinforced aluminum foams, the experimental results also show that on the basis of maintaining the original function of aluminum foams, the physical properties of the materials are further improved, and higher energy absorption, damping, and damping are achieved. Foam wall toughness aluminum foam material.

How to obtain a better sandwich structure, strengthen the bonding force between aluminum foam and other materials, enhance the performance characteristics of each material, or seek out a new structure, such as a multi-layered sandwich structure, is also a good s Choice.

In short, although aluminum foam has been studied in depth and has been applied in many other industries, it is still far from fully mature in the automotive industry. Currently, it is only used in some auto parts. However, as an excellent material, its application is far more than this. In the future, the combination between aluminum foam and various materials will be a trend.

summary:

As an excellent material, foam aluminum has a higher status in the automotive field. In the modern automobile industry where aluminum alloys are popular, it should receive more attention. Solving its cost and unity, finding a better method of compounding structures and materials may be the new direction of development for this material.